1. Field of the Invention
The present invention is relating to an AC-excited generator/motor apparatus and more particular to an apparatus suitable for improving the stability of an AC power system such as a variable-speed pumping-up power system and a fly-wheel generator/motor system.
2. Description of the Related Art
In a conventional AC-excited generator/motor apparatus as disclosed in Japanese Patent Kokoku Sho Nos; 53-7628 and 57-60645, the exciting current is controlled for controlling active and reactive power for the AC-excited machine. Such an apparatus is useful as an active power regulator or reactive power regulator having a characteristic of fast response without hunting or stepping out of synchronization.
A variable-speed pumping-up power generator system in which a cycloconverter is used as a frequency converter for AC excitation and a pump turbine is directly connected to an AC-excited synchronous machine is suitable for adjusting frequency of a power system as disclosed in Record of the 1988 Kansai-Section Joint Convention of Institutes of Electrical Engineers of Japan. A similar system is disclosed in National Convention of Institutes of Electrical Engineers of Japan, No. 1026, 1986 and Japan Electric Association, Journal, Pages 34-39, March 1986.
Measures for establishing cooperation between an AC excitation control device and a pump turbine guide vane control device are disclosed in Japanese Patent Kokai Sho Nos. 62-71497, 62-72498 and 62-282169.
Control of such an AC-excited generator/motor apparatus useful when it is shut off from an AC power system is disclosed in Japanese Patent Kokai sho 63-43599.
In the AC-excited generator/motor apparatus as disclosed in any of the above references, the control of AC excitation is carried out by using as a reference signal the phase of voltage of the AC power system. However, none of the references teaches or discloses the control of AC excitation which is still effective when the apparatus is shut off from the AC power system, resulting in disappearance of the reference signal for control.